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33SYNTHESIS OF SHS MEMBRANES BASED ON
MICA-LIKE STRUCTURE MATERIALS FOR LIQUID AND GAS
FILTRATION
V. I. Uvarov", A. R. Kachin", V. E. Loryan", V. S. Shustov", and M. V. TsodikovA
aMerzhanov Institute of Structural Macrokinetics and Materials Science, RAS, Chernogolovka, 142432 Russia
bTopchiev Institute of Petrochemical Synthesis, RAS, Moscow, 119991 Russia e-mail: uvar@ism.ac.ru; kachin@ism.ac.ru
DOI: 10.24411/9999-0014A-2019-10182
Man-made burden on the environment can lead to irreversible changes in the composition of natural water. In particular, surface and underground water sources are contaminated by substances of anthropogenic origin - heavy metal ions, nitrates, volatile organochlorine compounds, herbicides, pesticides, radionuclides, etc. [1, 2]. Therefore, the research aimed at purification of drinking water, in particular development of filter technologies using various materials, is relevant.
The process of self-propagating high-temperature synthesis (SHS) of materials, including porous, is energetically advantageous, since the heating of the charge, the synthesis and sintering of the final materials is not due to external heating, but due to the release of heat during chemical reactions between the components of the charge, which provides the possibility of propagation of the combustion wave.
A comparative analysis of characteristics of filters manufactured in different countries shows the expected advantages of SHS filters, especially multiple application after regeneration. It is impossible for the filters produced by traditional methods [3, 4].
Fluorophlogopite is known to have mica-like structure and a high ion-exchange capacity. It can be used for binding and preservation of heavy metal ions due to heterovalent replacement of Na+ ion by metal ions determining water hardness (Ca+, Mg+, Sr2+, Ba2+). It is possible to obtain porous material based on fluorophlogopite by the SHS method. Filters based on fluorophlogopite can be used for fine purification of air and process gases from aggressive dispersed micro-impurities and radioactive aerosols.
The aim of this study is to create highly efficient, corrosion-resistant SHS membranes for purification of liquids and gases both in industrial plants and for small installations that allow regulating the salt composition of water that is necessary for providing active human activity during its consumption.
Experimental methods. Quartz sand (SiO2), Karelian schungite, aluminum PAD-1 (GOST 6058-73), and magnesium MPF-3 (GOST 6001-79) were used as initial elements in the experiments. Recycled cryolite Na3AlF6 was used as a source of fluorine, potassium perchlorate KClO4 (TU 6-09-3801-76) - as an oxygen source. Some amounts (up to 15%) of iron and chromium oxides were introduced into the mixture as catalytically active additives. The quartz sand and schungite were crushed into powder of less than 150 and 50 p,m in ball drums. The particle size was measured using a MicroSizer 201 analyzer. The mixtures which can react in the SHS mode were used. The initial mixture composition was estimated by the following chemical scheme:
x (21.65SiO2 + 2.16Al + 8.64Mg + 8.5Na3AlF6 + 5.4KClO4) + y (21.6Shung + 4.3Mg + 1.1Al + 4.1Na3AlF6 + 1.4KClO4) ^ NaMgsSisAlO^ + KCl| (x + y = 100 %)
ÏSHS2019
Moscow, Russia
The initial billets of 40 mm in diameter and ~ 5 mm in height were sintered in the furnace at T = 930°C in the air of atmospheric pressure. The temperature was being raised during 1 h. The exposure time at 930°C was 10 min. The phase composition of the product was determined with CuXa radiation diffractometer DRON-3M. Metallographic studies were performed using an optical microscope Axiovert 200 MAT. The quantitative elemental composition of the phases was carried out using a Zeiss Ultra Plus high-resolution SEM with INCA 350 Oxford Instruments X-ray microanalysis system.
The porosity of the synthesized material was determined in accordance with GOST 2409-80. The size of the open pores of the synthesized material was determined according to GOST 26849-86. The concentration of chemical elements in tap water before and after filtration was determined by the atomic absorption method.
Experimental results. The appearance of the synthesized sample is shown in Fig. 1. The main phases of the synthesized material are those of spinel and fluorophlogopite in approximately equal mass fractions (Fig. 2). At the same time, the presence of unidentified lines indicates a more complex composition of the material.
Fig. 1. Appearance of the synthesized sample.
Fig. 2. Phase composition of the synthesized material.
Figure 3 demonstrates the fracture structure (3a) typical of mica-like structure materials and the porosity of the synthesized sample (3b). According to the analysis, the material porosity is 60 %, the open porosity is 45%. The measured value of open pores (according to GOST 2684986) in the synthesized material is 1-3 p,m. The sample bending strength is 5.5-6 MPa.
Fig. 3. Synthesized material structure.
Membranes with mica-like structure were obtained by the direct synthesis. Their pore size was 1-3.5 |im, porosity > 60%, open porosity was up to 45%. It was established that the bending strength of the obtained samples was 5.5-6 MPa. the specific surface area was 1.203 m2/g.
As a result of the work, laboratory devices were developed and experiments in water purification were carried out. Table 1 demonstrates the content of metal ions in the water before and after its filtration through the synthesized membrane. The results prove that the obtained sample of the filter purifies the tap water rather efficiently from the high content of heavy metal ions and reduces the water hardness by 30%.
Table 1. Content of Mg and Ca ions in the water before and after filtration.
, Concentration of chemical element in tap water, mg/l
Chemical
element Before filtration After filtration through the synthesized filter
16. 856
Mg 23.706 16.343
15.963
63.276
Ca 81.350 62.735
63.186
Conclusions
Membranes with mica-like structure were obtained by the direct synthesis. Their pore size was 1-3.5 |m, porosity > 60%, open porosity was up to 45%. It was established that the bending strength of the obtained samples was 5.5-6 MPa, the specific surface area was 1.203 m2/g.
Multiple regeneration of filters can be carried out by a reverse pulsed flow of the purified water, washing with solvent or high-temperature annealing. The investigation results can be used for development of production technologies of porous mica-crystalline filters for fine purification of water and technological gases from dispersed micro-impurities.
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